Suspected militants attacked a Company Operating Base (COB) of the Army at Niausa in Arunachal Pradesh early on Tuesday, an Army official said.
No casualty or damage to property was reported in the attack, which police sources said was likely to have been carried out by NSCN(K) insurgents.
A group of men fired 5-10 rounds from "ineffective" small firearms and lobbed a Lathode grenade at the COB at Niausa in Longding district at around 1.15 AM, Kohima based Defence spokesman Col Chiranjeet Konwer told PTI.
The sentries retaliated and the attackers fled, Konwer said.
"There was no human casualty or damage to properties of the COB. The retaliatory fire had to be controlled keeping in mind the safety of the villagers in the vicinity," the spokesman said.
Operations are being launched against the attackers, he said.
Police sources from Longding said the National Socialist Council of Nagaland (Khaplang), which is active in the district, was behind the attack.